When you have a large file or group of large files that you want to send to someone, but you don't want to clog up your Dropbox account and you don't have time to just drive over to your friend's house with a USB drive, Justbeamit is a new web service that lets you upload a file, get a private link and send it to a friend. When they open it, a private peer-to-peer download session will start and they'll grab the file from you over the web.
Justbeamit makes the process easy on purpose: all you have to do is drag and drop the file you want to share into your browser window, and the web app will give you the URL you can send to your friend. You'll be able to watch the progress while your file is uploaded and when it's finished, you'll see a "waiting" indicator, meaning the service is waiting for the recipient to download the file. When they visit the link, Justbeamit opens the connection between you and the recipient and lets them download the file.
The service is dead simple to use, and doesn't require that you sign up for an account of any kind. The only downside is that because the service is little more than a gateway, the sender can't leave the page until the download is complete and once both parties leave the page, the transfer link is useless, so if there's a problem, you'll have to start over. Even so, the service works and is incredibly easy to use.